Scientists classify comets and asteroids that pass within 28 million miles of Earth's orbit as near-Earth objects (NEOs). Asteroids that collide and break into smaller fragments are the source of most NEOs, and the resulting fragments bombard the Earth at the rate of more than 100 tons a day. Although the vast majority of NEOs that enter Earth's atmosphere disintegrate before reaching the surface, those larger than 100 meters

(328 feet) may survive the descent and cause destruction in and around their impact sites.

Furthermore, even smaller objects that disintegrate before reaching Earth's surface can cause significant damage. For example, in February 2013 an 18-meter (59 foot) meteor exploded 14.5 miles above the city of Chelyabinsk, Russia, with the force of 30 atomic bombs, blowing out windows, destroying buildings, injuring more than 1,000 people, and raining down fragments along its trajectory (see Figure 1). Recent research suggests that Chelyabinsk-type events occur every 30 to 40 years, with a greater likelihood of impact in the ocean than over populated areas, while impacts from objects greater than a mile in diameter are predicted only once every several hundred thousand years.

In 1992, NASA began conducting scientific workshops and research into the identification, characterization, and tracking of NEOs, as well as into potential mitigation strategies. NASA reported NEOs with a diameter greater than 1 kilometer (0.62 miles) posed the greatest hazard to Earth and predicted a comprehensive survey could identify most NEOs of this size within a decade.1In 1994, the House Committee on Science, Space, and Technology requested NASA identify and catalogue within 10 years the orbital characteristics of all comets and asteroids greater than 1 kilometer in diameter and in an orbit around the Sun that crosses the orbit of the Earth.2Four years later, NASA established a NEO Program Office to coordinate these efforts.3In addition, the NASA Authorization Act of 2005 required the Agency to implement a "program to detect, track, catalogue, and characterize the physical characteristics of near-Earth objects equal to or greater than 140 meters in diameter" and established a goal of cataloging 90 percent of these objects by 2020.4However, even with a ten-fold increase in the NEO Program budget in the past 5 years - from $4 million in fiscal year (FY) 2009 to $40 million in FY 2014 - NASA estimates that it has identified only about 10 percent of all asteroids 140 meters and larger. Moreover, given its current pace and resources, the Agency has stated that it will not meet the goal of identifying 90 percent of such objects by 2020.

We initiated this review to examine NASA's NEO Program and assess the Agency's progress toward meeting statutory and other Program goals. Specifically, we reviewed NASA's allocation and use of resources and plans for the future of the Program. Details of the review's scope and methodology are in Appendix A.